An oscillator circuit provided in, for example, a semiconductor integrated circuit continues to operate even if a system incorporating the semiconductor integrated circuit is on standby. Since the total power consumption of the system depends on the power consumption of the oscillator circuit, it is necessary to reduce the power consumption of the oscillator circuit in order to reduce the power consumed while the system is on standby.
In general, in many cases, an oscillator circuit is designed as part of a semiconductor integrated circuit. Also, it should be noted that semiconductor integrated circuits have been scaled down, and according to, for example, design rules for 65 nm, I/O voltage VDDI/O for driving input-output pins of each of semiconductor integrated circuits is, for example, 1.8 to 3.6 V.
In order that the power consumption of the oscillator circuit is reduced, the oscillator circuit is designed according to design rules for transistors in a core portion of a semiconductor integrated circuit. A drive voltage for the transistors in the core portion is, for example, 1.2 V which is lower than I/O voltage VDDI/O. Thus, I/O voltage VDDI/O is lowered to 1.2 V by a step-down circuit.